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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.util;

import java.io.InvalidObjectException;

/**
 * This class implements the <tt>Set</tt> interface, backed by a hash table
 * (actually a <tt>HashMap</tt> instance).  It makes no guarantees as to the
 * iteration order of the set; in particular, it does not guarantee that the
 * order will remain constant over time.  This class permits the <tt>null</tt>
 * element.
 *
 * <p>This class offers constant time performance for the basic operations
 * (<tt>add</tt>, <tt>remove</tt>, <tt>contains</tt> and <tt>size</tt>),
 * assuming the hash function disperses the elements properly among the
 * buckets.  Iterating over this set requires time proportional to the sum of
 * the <tt>HashSet</tt> instance's size (the number of elements) plus the
 * "capacity" of the backing <tt>HashMap</tt> instance (the number of
 * buckets).  Thus, it's very important not to set the initial capacity too
 * high (or the load factor too low) if iteration performance is important.
 *
 * <p><strong>Note that this implementation is not synchronized.</strong>
 * If multiple threads access a hash set concurrently, and at least one of
 * the threads modifies the set, it <i>must</i> be synchronized externally.
 * This is typically accomplished by synchronizing on some object that
 * naturally encapsulates the set.
 *
 * If no such object exists, the set should be "wrapped" using the
 * {@link Collections#synchronizedSet Collections.synchronizedSet}
 * method.  This is best done at creation time, to prevent accidental
 * unsynchronized access to the set:<pre>
 *   Set s = Collections.synchronizedSet(new HashSet(...));</pre>
 *
 * <p>The iterators returned by this class's <tt>iterator</tt> method are
 * <i>fail-fast</i>: if the set is modified at any time after the iterator is
 * created, in any way except through the iterator's own <tt>remove</tt>
 * method, the Iterator throws a {@link ConcurrentModificationException}.
 * Thus, in the face of concurrent modification, the iterator fails quickly
 * and cleanly, rather than risking arbitrary, non-deterministic behavior at
 * an undetermined time in the future.
 *
 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
 * as it is, generally speaking, impossible to make any hard guarantees in the
 * presence of unsynchronized concurrent modification.  Fail-fast iterators
 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
 * Therefore, it would be wrong to write a program that depended on this
 * exception for its correctness: <i>the fail-fast behavior of iterators
 * should be used only to detect bugs.</i>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <E> the type of elements maintained by this set
 * @author Josh Bloch
 * @author Neal Gafter
 * @see Collection
 * @see Set
 * @see TreeSet
 * @see HashMap
 * @since 1.2
 */

public class HashSet<E>
    extends AbstractSet<E>
    implements Set<E>, Cloneable, java.io.Serializable {

  static final long serialVersionUID = -5024744406713321676L;

  private transient HashMap<E, Object> map;

  // Dummy value to associate with an Object in the backing Map
  private static final Object PRESENT = new Object();

  /**
   * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
   * default initial capacity (16) and load factor (0.75).
   */
  public HashSet() {
    map = new HashMap<>();
  }

  /**
   * Constructs a new set containing the elements in the specified
   * collection.  The <tt>HashMap</tt> is created with default load factor
   * (0.75) and an initial capacity sufficient to contain the elements in
   * the specified collection.
   *
   * @param c the collection whose elements are to be placed into this set
   * @throws NullPointerException if the specified collection is null
   */
  public HashSet(Collection<? extends E> c) {
    map = new HashMap<>(Math.max((int) (c.size() / .75f) + 1, 16));
    addAll(c);
  }

  /**
   * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
   * the specified initial capacity and the specified load factor.
   *
   * @param initialCapacity the initial capacity of the hash map
   * @param loadFactor the load factor of the hash map
   * @throws IllegalArgumentException if the initial capacity is less than zero, or if the load
   * factor is nonpositive
   */
  public HashSet(int initialCapacity, float loadFactor) {
    map = new HashMap<>(initialCapacity, loadFactor);
  }

  /**
   * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
   * the specified initial capacity and default load factor (0.75).
   *
   * @param initialCapacity the initial capacity of the hash table
   * @throws IllegalArgumentException if the initial capacity is less than zero
   */
  public HashSet(int initialCapacity) {
    map = new HashMap<>(initialCapacity);
  }

  /**
   * Constructs a new, empty linked hash set.  (This package private
   * constructor is only used by LinkedHashSet.) The backing
   * HashMap instance is a LinkedHashMap with the specified initial
   * capacity and the specified load factor.
   *
   * @param initialCapacity the initial capacity of the hash map
   * @param loadFactor the load factor of the hash map
   * @param dummy ignored (distinguishes this constructor from other int, float constructor.)
   * @throws IllegalArgumentException if the initial capacity is less than zero, or if the load
   * factor is nonpositive
   */
  HashSet(int initialCapacity, float loadFactor, boolean dummy) {
    map = new LinkedHashMap<>(initialCapacity, loadFactor);
  }

  /**
   * Returns an iterator over the elements in this set.  The elements
   * are returned in no particular order.
   *
   * @return an Iterator over the elements in this set
   * @see ConcurrentModificationException
   */
  public Iterator<E> iterator() {
    return map.keySet().iterator();
  }

  /**
   * Returns the number of elements in this set (its cardinality).
   *
   * @return the number of elements in this set (its cardinality)
   */
  public int size() {
    return map.size();
  }

  /**
   * Returns <tt>true</tt> if this set contains no elements.
   *
   * @return <tt>true</tt> if this set contains no elements
   */
  public boolean isEmpty() {
    return map.isEmpty();
  }

  /**
   * Returns <tt>true</tt> if this set contains the specified element.
   * More formally, returns <tt>true</tt> if and only if this set
   * contains an element <tt>e</tt> such that
   * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
   *
   * @param o element whose presence in this set is to be tested
   * @return <tt>true</tt> if this set contains the specified element
   */
  public boolean contains(Object o) {
    return map.containsKey(o);
  }

  /**
   * Adds the specified element to this set if it is not already present.
   * More formally, adds the specified element <tt>e</tt> to this set if
   * this set contains no element <tt>e2</tt> such that
   * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>.
   * If this set already contains the element, the call leaves the set
   * unchanged and returns <tt>false</tt>.
   *
   * @param e element to be added to this set
   * @return <tt>true</tt> if this set did not already contain the specified element
   */
  public boolean add(E e) {
    return map.put(e, PRESENT) == null;
  }

  /**
   * Removes the specified element from this set if it is present.
   * More formally, removes an element <tt>e</tt> such that
   * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>,
   * if this set contains such an element.  Returns <tt>true</tt> if
   * this set contained the element (or equivalently, if this set
   * changed as a result of the call).  (This set will not contain the
   * element once the call returns.)
   *
   * @param o object to be removed from this set, if present
   * @return <tt>true</tt> if the set contained the specified element
   */
  public boolean remove(Object o) {
    return map.remove(o) == PRESENT;
  }

  /**
   * Removes all of the elements from this set.
   * The set will be empty after this call returns.
   */
  public void clear() {
    map.clear();
  }

  /**
   * Returns a shallow copy of this <tt>HashSet</tt> instance: the elements
   * themselves are not cloned.
   *
   * @return a shallow copy of this set
   */
  @SuppressWarnings("unchecked")
  public Object clone() {
    try {
      HashSet<E> newSet = (HashSet<E>) super.clone();
      newSet.map = (HashMap<E, Object>) map.clone();
      return newSet;
    } catch (CloneNotSupportedException e) {
      throw new InternalError(e);
    }
  }

  /**
   * Save the state of this <tt>HashSet</tt> instance to a stream (that is,
   * serialize it).
   *
   * @serialData The capacity of the backing <tt>HashMap</tt> instance (int), and its load factor
   * (float) are emitted, followed by the size of the set (the number of elements it contains)
   * (int), followed by all of its elements (each an Object) in no particular order.
   */
  private void writeObject(java.io.ObjectOutputStream s)
      throws java.io.IOException {
    // Write out any hidden serialization magic
    s.defaultWriteObject();

    // Write out HashMap capacity and load factor
    s.writeInt(map.capacity());
    s.writeFloat(map.loadFactor());

    // Write out size
    s.writeInt(map.size());

    // Write out all elements in the proper order.
    for (E e : map.keySet()) {
      s.writeObject(e);
    }
  }

  /**
   * Reconstitute the <tt>HashSet</tt> instance from a stream (that is,
   * deserialize it).
   */
  private void readObject(java.io.ObjectInputStream s)
      throws java.io.IOException, ClassNotFoundException {
    // Read in any hidden serialization magic
    s.defaultReadObject();

    // Read capacity and verify non-negative.
    int capacity = s.readInt();
    if (capacity < 0) {
      throw new InvalidObjectException("Illegal capacity: " +
          capacity);
    }

    // Read load factor and verify positive and non NaN.
    float loadFactor = s.readFloat();
    if (loadFactor <= 0 || Float.isNaN(loadFactor)) {
      throw new InvalidObjectException("Illegal load factor: " +
          loadFactor);
    }

    // Read size and verify non-negative.
    int size = s.readInt();
    if (size < 0) {
      throw new InvalidObjectException("Illegal size: " +
          size);
    }

    // Set the capacity according to the size and load factor ensuring that
    // the HashMap is at least 25% full but clamping to maximum capacity.
    capacity = (int) Math.min(size * Math.min(1 / loadFactor, 4.0f),
        HashMap.MAXIMUM_CAPACITY);

    // Create backing HashMap
    map = (((HashSet<?>) this) instanceof LinkedHashSet ?
        new LinkedHashMap<E, Object>(capacity, loadFactor) :
        new HashMap<E, Object>(capacity, loadFactor));

    // Read in all elements in the proper order.
    for (int i = 0; i < size; i++) {
      @SuppressWarnings("unchecked")
      E e = (E) s.readObject();
      map.put(e, PRESENT);
    }
  }

  /**
   * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
   * and <em>fail-fast</em> {@link Spliterator} over the elements in this
   * set.
   *
   * <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and
   * {@link Spliterator#DISTINCT}.  Overriding implementations should document
   * the reporting of additional characteristic values.
   *
   * @return a {@code Spliterator} over the elements in this set
   * @since 1.8
   */
  public Spliterator<E> spliterator() {
    return new HashMap.KeySpliterator<E, Object>(map, 0, -1, 0, 0);
  }
}
